Wave guide junctions



July 30, 1957 vb 4SDAIRIKI EI'AL WAVE GUIDE JUNcTroNs Filed May 16, 1.955

e of thev cited text.

United States Patent WAVE GUIDE JUNCTIONS Setsuo Dairiki, Weston, and Max Michelson, Newton, Mass., assignors to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware Application May 16, 1955, Serial No. 508,442

2 Claims. (Cl. S33- 9) Y This invention relates to Wave guide junctions suitable for use as duplexers, and more particularly to such junctions in the form of a T with the Velectrical advantages of Y-shaped junctions, and also to duplexing systems utilizing such junctions.

In applications such as pulsed radar, it is desirable to use the same antenna for both transmitting and receiving. For this purpose it is necessary that theV oscillator output be conveyed entirely to the antenna during transmission with a minimum of this energy reaching the receiver, and, in the interval between transmitted pulses, it is necessary that all the received energy reach the receiver and that thistake place over as wide a band of frequencies as possible. The simplest structure for this purpose is a T-shaped junction formed by adding a side arm of wave guide for the receiver to a straight section of transmission line which runs from the transmitter to the antenna with a TR or other switching device across the receiver branch to provide an apparent short circuit during transmission when properly positioned and matched in impedance. The wave guides could be joined in a plane parallel to either the E or the H vector of the energy propagated in both guides. It has been found that the junction is most efficient when made in the plane parallel to the E vector. Such junctions are illustrated in Fig. 7.6 and described on pages 269 and 270 of vol. 14 of the Radiation Laboratories series entitled Microwave Duplexers by Smullin and Montgomery. As indicated in the cited text, such T-shaped junctions are cheap to build, but cannot be operated eiiciently over a broad band of frequencies.

To overcome this diiculty and to provide a junction where the arms may be used interchangeably for connection to the antenna, the transmitter, or the receiver, a Y-shaped junction has been developed in which the arms make an angle with each other of 120 instead of the angles of 90 and 180 as is the case in the T-shaped junction. This type of junction has been found to be most eicient when the axes of the joined guides lie in a plane parallel to the H vectors of the propagated energy. Such a junction is illustrated in Fig. 8.16 and described on page 265 of the above-cited text. It has been found that such a junction is ditlicult to build to accurate dimensions at reasonable expense.

For this reason, a junction having the outward form of the T-shaped junction, but electrically the equivalent of the Y-shaped junction, has been developed with a T junction in the H plane and two reecting surfaces each parallel to the E vector of the propagated energy and i forming a 30 angle with, and on opposite sides of, the

receiver guide and two additional surfaces forming angles of 15 with the axis of the main guide mounted on the rear narrow wall of the main guide symmetrically about the axis of the receiver guide. Such a junction is illustrated in Fig. 7.8 and described on pages 273 and 274 A junction constructed in this manner has the electrical advantages of the Y junction with the mounting convenience of the T junction, but it is still diicult to build to accurate dimensions.

2,801,390 Patented July 30, 1957 lCC In the present invention the advantages of the Y junction are obtained by adding matching posts to the standard T junction formed in the plane parallel to the H vector of the propagated energy. One such post is mounted in the junction approximately on the center line of the receiver guide and perpendicular to the main axis of both guides. This post is positioned approximately a third of the width of the guide from the narrow wall opposite the junction. Two other posts are mounted in the main guide, each approximately on a projection of a side wall of the receiver guide perpendicular to the axis of both guides andspaced a sixth of the width of the guide from the back wall of the junction. These posts perform the function of the complicated rellecting surfaces in the modified T junction described above. It is much easier and cheaper to insert simple posts into a standard T junction than it is to construct the compound bends in the above-described structure. The structure of the invention therefore gives a simple and cheap construction having the same desirable electrical characteristics as the Y-shaped junction described above. l'

These and other features and advantages of the invention will become apparent from the following description taken in connection with the accompanying `drawing illustrating the invention wherein:

Fig. l is a top view of the junction of the invention;

Fig. 2 is a side view of the junction of the invention; and

Fig. 3 is a schematic diagram showing the junctions of the invention used in a duplexer system.

In Figs. l and 2 the reference numeral 10 designates a rst section of wave guide having wide walls 11 and narrow walls 12. The wide walls are parallel to the H vector of the propagated energy and the narrow walls are parallel to the electrical vector of the propagated energy. A second section of Wave guide 13 also having wide walls 14 and narrow walls 15 joins the first at an opening in a narrow Wall 12. The wide walls 11 and 14 of the guides 10 and 13 are in common planes. The H plane of the energy propagated in each guide and the axes of the two guides are at right angles at the junction. Three matching posts 16, 17 and 18 are mounted in the iirst section of Wave guide 10 perpendicular to the wide walls 11. One of said matching posts 16 is positioned on or close to the extended center line 20 of the second guide 13 and spaced from the narrow wall 12 opposite the junction a distance 2a that approximates a third of the width 6a of the wide walls 11. The two other matching posts are positioned each on a projection of the narrow walls of the second guide 13 as indicated by the lines 21 and 22 and spaced a distance a approximating a sixth of the width of the wide walls 11 from the narrow wall 12 oppo-site the junction.

In operation the junction acts very much like the Y junction described in the above-cited reference or the vestigial junction also described in the cited reference. In fact, the analogy is closer to this last-mentioned type of junction. The central post may be compared to the central point of the compound 4wedge inserted into' the T-shaped junction and the two side posts to the supplementary vertexes on either side of the main point of the wedge. Energy coming from one end of the guide 10 proceeds through to the other without any appreciable portion being diverted down the guide 13. On the other hand, energy coming from the other end of the guide 10 in the absence of energy coming from the first-mentioned end is propagated down the guide 13 with no appreciable portion being dissipated down the other end of the guide. Such a junction is most frequently used with appropriate switching devices such as TR and ATR tubes to produce a duplexing system in such applications as radar.

kof the wave guide.

Fig. 3 shows schematically such a duplexing system. The block 30 designates a transmitter and the block 31 an ATR device coupling the output of the transmitter 30 to one arm of the wave guide junction v32. This wave guide junction 32 is similar in construction to that shown in Figs. l and 2. This junction is formed of .two sections of wave guide 33 and 34 joined at `right angles with their wide walls lying in a common plane parallel to the H vector of the energy propagated in both vectors A receiver 3S is coupled to the short arm 34 through a switching device, such as a TR cavity 36. Three matching posts 37, 38 and 4t) are mounted within the guide 33 in the same manner as are-the posts 16, 17 and 18 of the junction shown in Figs. l and 2l. An antenna 42 is connected to the other end of guide 33. This antenna is shown as of the horn type; however, any type of rantenna may be used. ln operation, when the transmitter 3i) is on, a series short circuit is presented by the TR cavity `37 which is then conducting so that no energy is dissipated in the receiver branch guide 36 and all the transmitted .energy is propagated to the antenna 42 down the main section of wave guide 33. When the transmitter 30 ceases to operate, the TR cavity of device 37 no longer conducts and the posts 38, 40 and 41 match the impedance of the cavity and its associated receiver to that of the antenna, while mismatching the impedance of the ATR cavity 31 and the transmitter 30 to that of the antenna. practically all the energy from the antennay is propagated through the receiver branch line 34 and the TR kcavity 37 to the receiver 36.

The position of the matching posts 16, 1.7 and 1S of Figs. l and 2, and 38, 40 and 41 in Fig. 3 may be shifted somewhat from the optimum positions, as specified above, to permit the equipment to operate efficiently over as broad a band of frequencies as possible. The junction of the invention can be adjusted in this manner to operate over a wide band of frequencies at close to maximum eiciency. This result is obtained with a construction that is relatively cheap Vto build and simple to adjust.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended The result is that claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A wave guide junction comprising rst and second sections of rectangular wave guide joined with the wide walls of both guides parallel to a plane containing the axes of both sections and with their axes perpendicular to each other and an opening in the side wall of the first guide where the second guide joins, and a matching post mounted perpendicular to and electrically connecting the wide walls and spaced from the narrow wall of the iirst guide opposite the junction by a distance approximating a third of the width of the wide side of the guide, and a pair of matching posts each perpendicular to and electrically connecting the wide walls in a separate plane defined by a sidewall of said second waveguide Vat a distance from the narrow wall opposite the junction approximately a sixth of the width of the guide.

2. A wave guide junction comprising first and second sections of rectangular wave guide joined with the wide walls of both guides parallel to a plane containing the axes of both sections and with their axes perpendicular to each other and an opening in the side wall of thc first guide where the second guide joins, and Aa matching post of conductive material mounted perpendicular to and electrically connecting the wide walls and spaced from the narrow wall of the first guide opposite the junction by a distance approximating a .third of the width ofthe wide side of the first guide, and a pair of matching posts of conductive material each perpendicular to and electrically connecting the wide walls in a separate plane defined by a sidewall of said second waveguide at a distance from the narrow wall opposite the junction approximately a sixth of the width of thc guide.

References Cited in the file of this patent UNITED STATES PATENTS 2,619,539 YFano Nov. 25, 1952 2,640,877 Miller June 2, 1953 2,679,582 Edwards May 25, 1954 2,681,987 Farr june 22, 1954 2,685,065 Zaleski July 27, 1954 

